This invention relates to sulfur-absorbant compositions, the manufacture of sulfur absorbants and their use.
The removal of sulfur from fluid streams can be desirable or necessary for a variety of reasons. If the fluid stream is to be released as a waste stream, removal of sulfur from the fluid stream can be necessary to meet the maximum sulfur emission requirements set by various air pollution control authorities. Such requirements are generally in the range of about 10 ppm to 500 ppm of sulfur in the fluid stream. If the fluid stream is to be burned as a fuel, removal of sulfur from the fluid stream can be necessary to prevent environmental pollution. If the fluid stream is to be processed, removal of the sulfur is often necessary to prevent the poisoning of sulfur-sensitive catalysts or to satisfy other process requirements.
Various absorption compositions have been used to remove sulfur from fluid streams when the sulfur is present as hydrogen sulfide (H.sub.2 S). It has been proposed that the compound zinc oxide (ZnO) be used as a material for absorbing hydrogen sulfide, however, the material by itself lacks the properties necessary for being an effective commercially usable absorbing material. In order for an absorbent composition to be commercially usable, it must have a high sulfur-absorption capacity and sufficient mechanical strength to permit its use as a contact material that is placed as a bed within a contact vessel. Furthermore, it is important for the commercial viability of the absorbing material for it to have the ability to be regenerated, after becoming spent, numerous times without appreciable loss of the absorption power with respect to the sulfur compounds and without reduction of the mechanical strength. While zinc oxide in combination with certain porous media is an effective absorbent, the material does not possess many of the properties required for an effective, commercially viable absorption material.
One approach used to resolve the problems of inadequate mechanical strength and unregenerability is to add binders to the zinc oxide and porous media material. While various binders have been proposed, many have certain negative consequences from their use. One negative aspect from the use of a binder material is that it replaces a certain volume and mass of the active absorption material with an essentially inert material. Consequently, for a given absorption capacity, a larger volume of material will be required thus necessitating larger contact vessels for holding the material. Additionally, in many instances, the binder material can be more costly than the absorption material resulting in a more costly product based upon the capacity of the composition to absorb sulfur. Moreover, the use of certain binder materials, such as alumina (Al.sub.2 O.sub.3), cause sulfur dioxide (SO.sub.2) slippage by causing certain amounts of hydrogen sulfide in a fluid stream to be converted into sulfur dioxide and to pass along with a treated effluent stream.
An additional problem that has been encountered in the manufacture of absorption compositions is equipment wear caused by the abrasive nature of the absorption materials being manufactured. In certain attempts to produce commercial quantities of absorbent compositions, excessive equipment wear and downtime caused by the abrasive characteristics of the absorption material components have, in effect, rendered the production commercially unviable.